Cracks in RCC ? Let us find out more about them in this excellent reply given by Ms. Rakshita from Indore . She is studying in the same engineering college from which the author graduated in 1976 .
Answer by Rakshita Nagayach:
The various causes are:
• Structural cracks
1) Due to incorrect design
2) Faulty construction
• Non Structural cracks
1) Moisture changes: Shrinkage effect,depending on the water content, cement concrete and aggregates.
2) Thermal movement: Concrete made in hot weather needs more water for same work-ability and hence results in more shrinkage.
3) Elastic deformation
4) Creep: Building items such as concrete and brick work when subjected to a sustained load not only undergo elastic strain but also develop gradual and slow time dependent deformation known as creep or plastic strain.
5) Chemical reaction: Certain chemical reaction in building materials result is appreciable change in volume of resulting products and internal stresses are set up which may result in outward thrust and formation of cracks.
6) Foundation movement and settlement of soil: Buildings on expansion clays are extremely crack prone.
7) Vegetation: Large trees growing in the vicinity of buildings cause damage in all type of soil conditions. If the soil is a shrinkable clay, the cracking is severe.